by Jerry Oltion
Illustrated by Eldar Zakirov
The mood in the control room was tense. When everything depends on the next hour or so, people grow quiet and focused. In a little less than an hour, the DART spacecraft would arrive at the asteroid Didymos, and all their effort would go out in a final blaze of glory.
Priya Joshi and her partner in crime—and in practically everything else—Mark Anderson, shared a monitor at the end of the back row. They weren’t directly part of the mission, but as astronauts with extensive EVA training and experience navigating spacecraft, they were there to observe and learn and help if they could. Plus Priya was on NASA’s asteroid exploration team, an as-yet theoretical sub-group of astronauts who might someday actually venture out to one of the Solar System’s flying rocks, and this was her chance to see one up close. Really close.
It wasn’t every day that NASA whacked an asteroid with a half-ton space probe. DART was designed to test how much influence an impact would have on the asteroid’s orbit, but it was also proof of concept for much more ambitious missions to follow, some of which might be crewed depending upon what they discovered tonight. Didymos was an Earth-crossing asteroid with a two-year period, relatively easy to reach and relatively easy to return from after an extended stay. If NASA ever sent a mission out there, Priya planned to be on board.
The mission clock ticked over to 6:30. Forty-four minutes to impact. Didymos was a bright speck in the center of the field, still too small to show a disk. But the probe was approaching at over four miles per second, and as they watched, a dimmer speck separated from the bright one. Dimorphos, Didymus’s tiny moon. That was the actual target. DART would strike it head-on as it swung around in its orbit, slowing it down by a smidgen, enough for telescopes on Earth to detect the difference in its period after a few more orbits. And that sudden slowdown would change the orbit of the larger companion by an even smaller smidgen. Not enough to matter, but it was a proof-of-concept mission, a demonstration that we could alter the orbit of an asteroid if we needed to.
A cheer filled the room as the two bright dots separated. “Right on schedule,” Mark said. So far the mission was going nominally. It was entirely automated at this point, with the probe thirty-six light-seconds away, so if anything went wrong, there would be little the controllers could do to correct it.
“It’ll be switching guidance from Didymos to Dimorphos,” Priya said. And as she spoke, the view gave a little jerk. “That was the thruster.”
The mission communicator a few stations down the row said, “The probe has achieved a navigation lock on Dimorphos. All systems are ‘go.’ Forty-one minutes to impact.”
Priya said, “That means the probe is . . . almost exactly ten thousand miles out.”
Mark laughed. “Stop showing off!”
Priya felt herself blush. “The numbers are easy. Four miles per second, sixty seconds in a minute, forty-one minutes.”
Mark said, “Four miles per second sounds fast, but it’s less than orbital speed. The ISS is going faster.”
“But the ISS isn’t going to smack into an asteroid.”
“I hope not,” Mark said. “I’m going up next year.”
She fist-bumped him. “To a great mission.” She’d been up once, three years ago, but wasn’t even on the schedule again.
“You’ll get another shot at it,” he said.
Priya just shrugged. To be honest, another tour on the ISS wasn’t high on her list of priorities. She wanted the Moon, or an asteroid like Didymos, or even Mars. To actually go somewhere, see something new, accomplish something nobody had done before.
The two specks drew apart on the monitor as the probe closed in. Mark said, “I read somewhere that the number of Earth-grazing asteroids that are binary is way higher than the number of binaries out in the main asteroid belt. Weird statistic.”
Priya said, “It’s the YORP effect. Sunlight on a rotating body makes it spin faster, and it eventually breaks apart. Sunlight is stronger on near-Earth asteroids than on main belt asteroids.”
Mark laughed. “I was just going to guess that.”
“Sure you were.”
Priya took a sip of coffee and kept the mug in her hand for warmth. She had become shivering cold in the last few minutes.
They watched the asteroids draw apart, Didymos finally becoming a disk rather than just a point of light. It was roughly spherical, with boulders and depressions more or less at random. Dimorphos was much smaller, only five hundred feet, a fifth the size of Didymos, so they didn’t see detail until just a couple minutes before impact. When they did, all that stood out was just a bright spot on a surprisingly smooth, round surface.
“That’s weird,” Priya said. “It’s more spherical than Didymos. You’d expect the smaller one to be more ragged. Less gravity to pull things together.”
It was growing fast now. Didymos slid off to the side of the screen, leaving Dimorphos dead center. The bright spot began to take on shape, but that shape was perfectly round. Round with a blister dead center. Sunlight angling in from the side made it obvious that they were looking at a dome. A dome with round ports, dish antennae, and angled black solar panels.
Voices raised all around the control room. “What the hell! That’s artificial! Who put that there?”
Priya said, “Abort! Abort! Oh, shit.” She set her coffee mug down hard on the desk, sloshing it, but didn’t look down. She couldn’t tear her eyes away. The probe sailed straight onward, the abort signal crawling along after it at the speed of light, if one had been sent at all. Nor could the thrusters move the probe far enough in the few seconds left even if the signal had been instantaneous.
The guidance system did an impeccable job: The probe struck dead square in the center of the dish antenna mounted atop the domed outpost.
The video winked out upon impact, but DART had deployed a cubesat ten days earlier that had drifted behind to watch the results. LICIA got clear video of the expanding debris cloud. Shrapnel erupted outward from the surface, blasting into space in a tight cone—aimed directly at LICIA. There was just time to make out some of the tumbling girders and twisted metal panels before LICIA ran into the debris cloud and the signal stopped.
The control room erupted in pandemonium. Among the dozen other voices, Priya said to Mark, “The facility must have been dug into the asteroid a ways. If it was completely on the surface, the explosion would have blown everything out sideways. But the ejecta mostly came straight back along the incoming path, which means it was directed like rocket exhaust. My guess is that there were at least a dozen basement levels.”
Greg, the tech at the station next to her nodded. “It reminds me of the 9/11 attacks on the World Trade Center. The planes just disappeared into the buildings for a second or two before the explosions. The force was all outward, and it came from deep inside.”
Priya had been in grade school when that happened, but she remembered the video as if it had been yesterday. “Yeah,” she said, “The structure was mostly empty space. And that’s what it looks like we have here. The explosion didn’t really take off until DART hit bottom.”
Mark said, “That implies habitation. If it was a robotic installation, there wouldn’t be any need for empty space.”
“I didn’t see any bodies in the debris,” Greg said.
“It’s hard to tell,” Mark said, “but it doesn’t look like there was atmosphere in there. The debris was all solid stuff. Hardware.”
“And rock, there at the end,” said Priya. She tapped the video slider on her monitor and dragged it back a quarter inch, replaying the impact and its aftermath. Amid the metal debris, several obvious chunks of ragged asteroid material also flew out. Priya said, “That’s from the ground floor.”
It’s amazing what you can learn by watching something be destroyed, she thought. They were like physicists examining particle tracks in an atom smasher, deducing what had to have created the patterns they saw.
“Who the hell could have put that there?” someone down the row asked. “And why?”
“Elon?” Mark said.
Greg said, “Not likely. Something like this would have taken a major launch effort. He’d never have been able to keep it secret.”
“China, then?” Priya said.
“North Korea,” someone else said, and everyone laughed. But it was a hollow laugh. Someone had obviously put an outpost on Dimorphos, and the only good reason for doing that was the same reason for the DART mission: to nudge the binary pair into a different orbit. But if they were doing it in secret, then presumably they intended to shift it onto a course that would impact Earth.
* * *
Priya was in the Astronaut Office first thing in the morning. “I volunteer for the mission,” she said.
To his credit, the director didn’t ask “What mission?” He just said, “We’re not even close to assigning a crew yet.”
“I know that. But when you do, I’m your best candidate. It’s a two-year trip out and back, so supplies are going to be our biggest concern. I weigh a hundred and ten pounds and can thrive on a twelve hundred calorie diet. Probably less in freefall. And I’m already in the asteroid rendezvous group. And my Ph.D. thesis was on the search for extraterrestrial intelligence.”
He raised his eyebrows. “You think that was an ET outpost?”
“When you’ve eliminated the impossible, whatever’s left . . .”
“Yeah, right. I think we’re far from proving that someone from Earth couldn’t have set that up. But yes, you’re on the short list. Because we’re probably going out there no matter who turns out to be the culprit.”
Priya thanked him and let herself out, nearly bumping into Mark in the hallway. “Beat you to it,” she said.
Mark laughed. “We’ll see how much that matters when the time comes. I get the feeling there’s going to be a lot of money thrown at this one.”
“Yeah, maybe so. Good luck to both of us, then.” Priya gave him a quick hug. But she knew it was a one-person mission, and she knew who was going.
* * *
In the following days, astronomers turned practically every telescope on Earth—and off it—on Didymos and its mysterious moon, but saw nothing remarkable. Radar picked up sparkles of reflection from the debris still moving away from the explosion, but no motion on the surface. Nobody radioed for rescue, and nobody on Earth claimed responsibility for the installation. Dimorphos’s orbit had shortened by about a hundred and thirty seconds, nearly twice the predicted amount, presumably due to the focusing effect on the ejecta plume.
At least there wasn’t an advancing fleet of vengeful aliens. But as the days drew on without answers, speculation ran rampant on the internet. It was the Russians. It was Martians. It was Satan. It was a leftover spacecraft from the fleet that had seeded the Earth with life billions of years ago. And of course it was responsible for COVID-19, global warming (which was nonetheless a myth), and inflation.
Then astronomers noticed that something had detached from another Earth-grazing asteroid about forty million miles away and was heading toward Didymos. Under power. There was no visible rocket exhaust, but the thing was accelerating continuously at 2.5 gees. In fourteen hours it had covered half the distance, then began decelerating at the same 2.5 gees.
If there had been fuel involved, the acceleration would have increased as the mass of the spacecraft decreased. Maybe the aliens—for nobody seriously doubted anyone else was behind it now—had an upper limit that they could withstand and had throttled down as their mass decreased. Or maybe they were using entirely different technology.
Maybe they were from Jupiter, which maybe not coincidentally had a surface gravity of 2.5 gees. Or maybe they just wanted to make us think they were from Jupiter.
Maybe, maybe, maybe. Nobody knew anything for sure.
Debate raged over whether to contact the aliens or not, but it was a moot point. Practically every nation made a clandestine attempt, but none were successful. Either the aliens weren’t listening or weren’t interested in responding.
There had already been a follow-up mission in the works. Called Hera, it was the second half of AIDA, the “Asteroid Impact and Deflection Assessment” program that Priya had been involved in for years. Hera was due to launch in 2024 and rendezvous with Didymos in late 2026 or early 2027.
The only way to speed up an interplanetary transfer is with sheer power. If you’ve got the thrust for it you can shoot straight for your target and get there in weeks rather than months, but it takes a phenomenal amount of fuel. Nobody on Earth had a space drive that could keep up 2.5 gees of thrust for over a day, but SpaceX had a rocket they once called the Big Falcon Rocket, later renamed “Starship” when people realized what BFR really stood for, and it had already made several successful flights. It was designed to carry people to the Moon and to Mars; NASA suggested putting the Hera probe on a stripped-down Starship and sending it out to Didymos at top speed. It would still take several months, and the rendezvous would be at the far point in Didymos’s orbit, and the probe couldn’t go into orbit around the asteroid as originally planned, but it would get there years earlier and could at least send photos of what the aliens were up to.
And humanity collectively shivered in fear as they waited. There were over a dozen binary Earth-grazing asteroids, and it was a safe bet that every one of them had an alien outpost. None of them were on orbits that would bring them truly close to Earth within the next century or more, but with engines capable of keeping up 2.5 gees of thrust indefinitely, it wouldn’t take long to alter one’s orbit until it was on a collision course.
Priya lobbied for a crewed mission to follow, no matter what Hera discovered. Surprisingly, NASA agreed, perhaps worrying that SpaceX would do it on their own if they didn’t. Or China. Or Russia. Or North Korea. It was imperative that the U.S. be first.
But of course that meant asking Congress for the money.
* * *
The hearing was a joke. But after the midterm elections, Congress itself was a joke. The hearing started out simple enough, with questions like “Why can’t we just aim the James Webb telescope at it?” (Followed by the inevitable grumble: “We spent enough on the damned thing, it ought to be useful for something.”)
Priya, as the spearhead behind the mission—and because Congresspeople liked being photographed with astronauts—was NASA’s representative. She answered with the truthful observation that at Dimorphos’s distance, even the Webb couldn’t see the level of detail they needed.
What could we possibly do with a manned mission that we couldn’t do with robots? Adapt to what we find there.
What do you expect to find? We don’t know. That’s why we need to go look.
How do you propose to stop them once you get there?
And so on. It was clear from the start that the conservatives wanted someone to blame and someone to bomb, while the liberals wanted to convene a panel of experts who would study the situation for a decade and make a recommendation. And of course there were the grandstanders who asked brilliant questions like “Why didn’t we know about this beforehand?”
To which Priya merely replied, “Congressional budget cuts,” and let the silence linger.
Then the representative whom Priya had come to think of as the Honorable Stupid Son of a Bitch from the State of Ignorance asked, “How many men does NASA propose to send?”
Priya said, “One. And it’ll be a woman. Me.”
“You,” he said flatly. “A little slip of a brown girl.”
She bit her tongue. Took a deep breath. “An experienced astronaut who has extensively studied both extraterrestrial contact and asteroids. And who can live on twelve hundred calories a day. Which is a vital consideration for a mission of this duration,” she added for those who hadn’t been paying attention earlier.
Congressman Stupid cleared his throat and said, “No offense, Miss Gupta, but if we approve this boondoggle, we’ll be sending a man up there. A white man.”
A murmur swept through the chamber, but there was no bang of the gavel, no outcry of protest. So Priya said, “No offense, Congressman, but if you can say that and expect to be reelected, then we are all well and truly screwed, alien invasion or no.”
* * *
Mark cooked dinner for her that night. The TV was off. Neither of them wanted to hear the outcry from the conservatives accusing her of disrespect for the government that they showed no respect for, either, nor from the religious nuts who were already accusing her of making a pact with the devil, nor from the liberals who wanted to spend the money on vaccines and food for starving nations. Priya didn’t even want to think about it at the moment, but she couldn’t put it out of her mind.
Halfway through the meal, a delightful shrimp scampi on linguini with garlic toast on the side (“Good thing we’re both eating this or there’d be no smooching you for a week.”), she said, “You know, I’m beginning to wonder if I want to go out there after all. All the evidence seems to point toward hostile aliens bent on wiping out humanity before we can get a foothold outside the Solar System. What could I possibly accomplish besides setting them off even more than we have already?”
“You could make contact,” Mark said. “We need to do that whether they’re hostile or benevolent. We need to find out what they’re doing and why.”
“They’re moving asteroids around. That much is obvious. And as for why, I think that’s pretty obvious, too. Why else are so many doubles in Earth-crossing orbits?”
Mark considered that for a bite or two, then said, “Why do none of them come closer than a couple of million miles? With no impacts in the foreseeable future? If whoever’s out there wanted to be able to smack us down on a moment’s notice, you’d think they’d keep one ready to go.”
“So you think they’re just hanging out to watch us and using the asteroids to sweep in for a closer look every now and then?”
“Maybe. Or maybe they’re keeping the asteroids away. Maybe they’re watching over us, not just watching us.”
“That would be nice if it were true. But why don’t they answer our hail now that we know they’re there?”
He took a sip of wine. “Could be a test. We have to be able to reach them before they’ll respond.”
She snorted. “Oh, we reached them all right. You’d think that would have been enough.”
“You know what I mean. Columbus didn’t reach the new world by sending a message in a bottle. He had to come here himself.”
“And live to tell the tale.”
“You’ll make it.”
“Or you will. Senator Shithead isn’t the only misogynist racist in Congress. I probably killed my chance of a mission anywhere, much less to Dimorphos.”
Mark shook his head. “Nonsense. You’re the most qualified, most logical choice. Of course you’ll go.”
* * *
But when the mission was approved and the crew announced, it was Mark’s name at the top of the list, with Priya as backup.
She spent a day sulking, and another day feeling guiltily relieved, then she put aside her anger and her grief and her anxiety and helped Mark train for the flight. He insisted that she train right alongside him, because something could happen to him at the last moment and she could wind up going after all.
Whoever went would be riding in a modified Starship crew module. The thing was as big as a bus, with plenty of room for a couple dozen people if they were just going to the Moon and back, but for the extended trip to Dimorphos, every cubic foot of space would be taken up with food and oxygen and supplies to keep even a single person alive. The margin was tight with Mark’s extra mass, but doable. With Priya it would be a breeze.
The Hera mission swept outward. The faltering economy improved as people, convinced humanity was doomed, spent their savings on sports cars, boats, vacations, and lots and lots of survivalist supplies. Priya wryly noted that there was enough high-velocity lead being stockpiled in underground bunkers to deflect Didymos if it was all fired at the asteroid. She got hate mail and death threats for that, but she had been getting those for months now.
Hera reached the asteroid and sent back a flyby image of a dome under construction that looked just like the one that DART had smashed. Little creatures or robots or something dotted the surface of the asteroid, but they were only a foot or so long, too small to show up well in the images. Were they truly space aliens, lifeforms that lived in vacuum? Nobody knew. But it was clear they were rebuilding their outpost.
Not long afterward, astronomers noticed something odd: Dimorphos acquired a wobble in its orbit. It was speeding up as it swung around in the direction approaching Earth, and slowing down on the other side, falling closer to Didymos when it was around behind it and rising up higher when it was on the Earth-facing side. Then they realized it wasn’t Dimorphos’s orbit that was changing, but Didymos itself, the big asteroid. But it was moving onto a path that took it even farther from Earth than before. The aliens were moving it away from the Earth, not toward it.
The difference was only a few thousand miles; an almost insignificant amount on the scale of the Solar System, but it clearly meant something. But what? A warning? A peace offering? A thumbed nose?
“They’re probably testing their repairs,” Priya said to an interviewer who asked her opinion. Of course the news story twisted her words, proclaiming “Aliens test asteroid-moving ability in preparation for attack on Earth!”
The Starship project proceeded apace. Fuel flights rocketed into orbit, stockpiling propellant for the long burn. The crew module was loaded with supplies, including thousands of hours of movies, thousands of digital books, and thousands of hours of music, in part to trade with the aliens if cultural exchange was possible, but mostly to keep the passenger sane on the long way out there.
And three days before launch, Mark developed vertigo.
“You’re what?” Priya demanded when he told her. They were both in his bed, where she’d given him a hero’s send-off for most of the night.
She laughed. “You’re shagged out,” she said.
“No, I mean it. Everything is swirling around.” He tried to sit up, but twisted around and fell heavily back into the bed. Then he turned his head sideways and threw up.
“Don’t choke!” Priya pushed him hard over so he was on his side. “Breathe out first!”
He coughed, gasped, coughed, then took a deep breath. “Gah. Get a towel.”
She grabbed two from the bathroom, threw one over his mess, and handed him the other. “Maybe it’s food poisoning,” she said. They had been eating well in his last few days on Earth.
“Maybe.” He wiped his face and tried again to sit up. She helped him upright, but he had to close his eyes to keep from throwing up again. “Everything’s swirling around,” he said. “Fast. Teacup-ride fast.”
“That’s not good.”
And indeed it wasn’t. When they finally got him to the flight surgeon, a half-full barf bag and many dry heaves later, the flight surgeon diagnosed a swollen inner ear. “I hate to break it to you, bud, but you’re not flying in that condition.”
“How long before the swelling goes down?” Mark asked.
“A week, maybe two. But that’s not the real issue. Once this sort of thing develops, you never know when it’s going to happen again. And the natural rush of fluid to the head in microgravity will just make it worse.”
“So my career is shot.”
“Maybe not. There are medications you can take. Surgery if that doesn’t work. Alan Shepard beat it and made it back into space, and you can, too. But not in three days time.”
Mark turned—carefully—to Priya. “See,” he said, laughing softly. “I told you it’d be you.”
“Not like this!” she said. “I don’t want to take your place!”
But there was little choice. Mark was grounded, and she was next in line.
The death threats became more serious. Her entire apartment building had to be evacuated after three separate drive-by shootings. She had to bunk in the crew quarters at NASA. Even Mark had to stay there, as the internet filled with conspiracy theories that he had “chickened out and passed the torch to his n—”
“I sometimes wonder if we’d be better off with alien overlords,” he said sadly on the eve of her departure.
“Maybe I’ll ask them to invade,” Priya said. “If they aren’t already planning to.”
Copyright © 2022. Shepherd Moons by Jerry Oltion